Communication devices and methods with beamforming training

ABSTRACT

A communication device for RF-based communication with another communication device. The communication device comprising antenna circuitry configured to transmit and receive RF signals and beamforming circuitry configured to perform beamforming and to control the antenna circuitry in a beamforming training phase to transmit and/or receive RF signals using one or more selected directive beams. The beamforming circuitry is configured to perform beamforming training by controlling the antenna circuitry i) to transmit data using at least one first directive transmit beam, wherein the other communication device is configured to listen using a first directive receive beam, said data including a second transmit beam information, and ii) to subsequently listen using a predetermined second directive receive beam for a response from the other communication device.

BACKGROUND Field of the Disclosure

The present disclosure relates to different communication devices, suchas a mobile station and an access point, which are configured forRF-based communication with each other. The present disclosure furtherrelates to corresponding communication methods.

Description of Related Art

Communication systems in the 60 GHz frequency range suffer from strongfree space path loss, which increases with frequency. For instance, a 60GHz communication system has roughly 22 dB higher attenuation comparedto a communication system operating at 5 GHz. To overcome the increasedpath loss, 60 GHz or any mmWave communication system employsbeamforming, i.e. transmitter and/or receiver feature a steerablephased-array antenna (PAA), which can form directive beams towards theother communication device. Such beams have typically a high directivityand are spatially very narrow. The directivity in main directionincreases with the number of antenna elements per PAA. In contrast, thehalf-power beam width (HPBW) defines the spatial width of a patterndecreases with increasing number of antennas. Thus, the more antennasper PAA, the higher the directivity and the smaller the HPBW. In orderto make use of the PAA directivity for communications, beam alignment iscrucial and of high importance for mmWave communication systems and RFcommunication systems, methods and devices in general.

There is a need in such communication systems to yield higher antennagain in an association phase, thus increasing the AP coverage andenabling long-range association and data transmission. Furthermore, itis desired to reduce the collision probability among STAs (firstcommunication devices) during association phase.

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventor(s), to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentdisclosure.

SUMMARY

It is an object to provide communication devices and correspondingcommunication methods yielding a higher antenna gain, enablinglong-range association and data transmission, and/or reducing thecollision probability in association phase.

According to an aspect there is provided a (first) communication devicecomprising

-   -   an antenna circuitry configured to transmit and receive RF        signals, and    -   a beamforming circuitry configured to perform beamforming and to        control the antenna circuitry in a beamforming training phase to        transmit and/or receive RF signals using one or more selected        directive beams, wherein the beamforming circuitry is configured        to perform beamforming training by controlling the antenna        circuitry        -   i) to transmit data using at least one first directive            transmit beam, wherein the other communication device is            configured to listen using a first directive receive beam,            said data including a second transmit beam information, and        -   ii) to subsequently listen using a predetermined second            directive receive beam for a response from the other            communication device, which is configured to transmit, if            the data transmitted in step i) have been received, a            response using a second directive transmit beam indicated by            the second transmit beam information.

According to a further aspect there is provided a (second) communicationdevice comprising

-   -   an antenna circuitry configured to transmit and receive RF        signals,    -   a beamforming circuitry configured to perform beamforming and to        control the antenna circuitry, in a beamforming training phase,        to transmit and/or receive RF signals using one or more selected        directive beams, wherein the beamforming circuitry is configured        to perform beamforming training by controlling the antenna        circuitry        -   i) to listen using a first directive receive beam for data            transmitted by the other communication device using at least            one first directive transmit beam, said data including a            second transmit beam information, and        -   ii) to subsequently transmit, if the data transmitted in            step i) have been received, a response using a second            directive transmit beam indicated by the second transmit            beam information, wherein the other communication device is            configured to listen using a predetermined second directive            receive beam.

According to still further aspects corresponding communication methods,a computer program comprising program means for causing a computer tocarry out the steps of the methods disclosed herein, when said computerprogram is carried out on a computer, as well as a non-transitorycomputer-readable recording medium that stores therein a computerprogram product, which, when executed by a processor, causes the methodsdisclosed herein to be performed are provided.

Embodiments are defined in the dependent claims. It shall be understoodthat the disclosed methods, the disclosed computer program and thedisclosed computer-readable recording medium have similar and/oridentical further embodiments as the claimed devices and as defined inthe dependent claims and/or disclosed herein.

One of the aspects of the disclosure is to provide associationbeamforming training, which applies directive beams on least the secondcommunication device (AP), preferably on both communication devices (APand STA). This yields an increase in link budget during the associationphase, which can be exploited to extend association range, i.e. longrange association beamforming training. Thus, first communicationdevices being far away from the second communication device can discoverand join the basic service set (BSS) of that second communicationdevice. Further, it is proposed to modify channel access during theassociation beamforming training if reciprocity can be assumed. Thisreduces the collision probability between first communication devices byexploiting their inherent spatial beam separation.

In the following, the terminology of WLAN systems is used, i.e. there isa station (STA) as an example of a first communication device and asingle central network access point (AP) or personal basic service setcontrol point (PCP) (generally referred to as AP herein; WLANterminology sometimes uses the abbreviation PCP/AP) as an example of asecond communication device, wherein the first and second communicationdevices may also be called transmitter and receiver. Both communicationdevices intend to exchange data wirelessly in the 60 GHz (mmWave)frequency band. However, this invention is applicable to any other RFcommunication system employing beamforming such as mmWave LTE.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a schematic diagram of a communication system includingfirst and second communication devices;

FIG. 2 shows a diagram of a transmission interval as described inIEEE802.11ad;

FIG. 3 shows a diagram of conventional association beamforming training;

FIG. 4 shows a diagram of a beacon transmission interval;

FIG. 5 shows a diagram of a first embodiment of association beamformingtraining with a single STA;

FIG. 6 shows a diagram of a second embodiment of association beamformingtraining with a two STAs;

FIG. 7 shows a diagram of a third embodiment of association beamformingtraining with a two STAs employing reciprocity;

FIG. 8 shows a diagram of a Beacon Interval Control Field;

FIG. 9 shows a diagram of beacon frame body structure;

FIG. 10 shows a diagram of a simple association beamforming controlfield; and

FIG. 11 shows a diagram of an advanced association beamforming controlfield.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, FIG. 1shows a schematic diagram of a communication system including firstcommunication devices 1, 3 (stations STA1, STA2) and a secondcommunication device 2 (an access point AP). Each of the firstcommunication devices 1, 3 comprises an antenna circuitry (sometimesalso called antenna unit) 10, 30 configured to transmit and receive RFsignals, and a beamforming circuitry (sometimes also called beamformingunit) 11, 31 configured to perform beamforming and to control itsantenna circuitry 10, 30. Similarly, the second communication devices 2comprises an antenna circuitry 20 configured to transmit and receive RFsignals, and a beamforming circuitry 21 configured to performbeamforming and to control its antenna circuitry 20. More details oftheir operation will be described below.

Communication systems in the 60 GHz frequency range suffer from strongfree space path loss a_(fs) which increases with frequency:

a _(fs)[dB]=−147.55 dB+20 log₁₀ f+20 log₁₀ d

This formula above gives the free space path loss in dB as a function offrequency f and link distance d. Apparently, a 60 GHz communicationsystem has roughly 22 dB higher attenuation compared to a communicationsystem operating at 5 GHz.

To overcome the increased path loss, 60 GHz or any mmWave communicationsystem employs beamforming, i.e. transmitter and/or receiver feature anantenna circuitry, e.g. a steerable phased-array antenna (PAA), whichcan form directive beams towards the another communication device. Suchbeams have typically a high directivity and are spatially very narrow.The directivity in main direction increases with the number of antennaelements per PAA. In contrast, the half-power beam width (HPBW) definesthe spatial width of a pattern decreases with increasing number ofantennas. Thus, the more antennas per PAA, the higher the directivityand the smaller the HPBW. In order to make use of the PAA directivityfor communications, beam alignment is crucial and of high importance formmWave communication systems.

In the following description of exemplary embodiments, the terminologyof WLAN system will be used, i.e. there is a station (STA) and a singlecentral network access point (AP) or personal basic service set controlpoint (PCP), i.e. the term AP as used herein shall be understoodgenerally to reference either an AP or a PCP (also referenced as PCT/APsometimes in WLAN terminology). Both intend to exchange data wirelesslyin e.g. the 60 GHz (mmWave) frequency band. However, this disclosure isnot limited to this frequency band, but is applicable to any othercommunication system employing beamforming such as mmWave LTE forexample.

This disclosure particularly addresses the association phase (alsocalled beamforming training phase or association beamforming trainingphase) during which STAs discover and associate to an AP. This phase isin particular challenging since initial beam alignment needs to beperformed.

FIG. 2 shows a diagram of a transmission interval as described inIEEE802.11ad. The beacon interval (BI) is continuously repeated and thebeacon header interval (BHI) holds all phases with respect toassociation. The actual data transfer occurs in data transmissioninterval (DTI). Since it is desired to keep DTI long compared to theBHI, the association beamforming training (A-BFT) phase and theannouncement transmission interval (ATI) in BHI can be occasionallyturned off, which is indicated in beacon frames sent during BTI.

Generally, according to IEEE802.11ad during a beacon transmissioninterval (BTI), the AP transmits identification data over variousdirective beams which have their main directivity in different spatialdirections. An STA listens to the medium, e.g. with an (quasi)omni-directional (also called “quasi-omni” hereinafter) or wide beamantenna, i.e. no directive pattern is applied. Once a STA receives theAP identification data, it remembers the sector ID which has beenapplied for this message. Furthermore, it (e.g. randomly) chooses a timeslot to transmit in the opposite direction (STA→AP) during associationbeamforming training (A-BFT) phase which follows subsequently to theBTI. In A-BFT, the STA transmits data with various directive beams tothe AP, which listens with an (quasi) omni-directional antenna. The STAtransmit data holds the best sector ID of the previous BTI. When the STAstops transmitting and the AP successfully received at least onemessage, the AP confirms reception including the STA sector which wasreceived in best quality (e.g. highest SNR). This message is transmittedvia the beam corresponding to the best sector ID indicated in previousA-BFT phase. The actual association procedure takes place in thefollowing announcement transmission interval (ATI). In the ATI, the bestbeams indicated by best sector IDs of BTI and A-BFT are employed.

In A-BFT, several STAs can compete for channel access. Therefore, theA-BFT is split in serval slots as depicted in FIG. 3, which shows adiagram of conventional association beamforming training. Here, theA-BFT is exemplarily split in 4 slots where STAs can respond. STAs whichwould like to associate with the AP choose randomly a single slot. Thisreduces the likelihood of a collision. In case a collision happens, theAP is able to detect and it avoids sending the SSW feedback frame whichis a reception confirmation. In case the SSW feedback is sent, it holdsinformation about the best transmit sector ID of the STA. STAs notreceiving the SSW feedback choose randomly a further A-BFT slot whichcould be even in an upcoming BI. The actual sweep of different antennasectors within a single A-BFT slot is done in the SSW frames. Each SSWframe is transmitted with a distinct antenna sector which has a sectorID label indicated within the same SSW frame.

The above described operation has the drawback that association happensin directive-to-omni (D2O) mode which allows for less antenna gaincompared to a directive-to-directive (D2D) mode. Hence, according to thepresent disclosure an association phase employing D2D yielding higherantenna gain in association phase is employed, thus increasing the APcoverage and enabling long range association and data transmission.Furthermore, double directive beamforming allows for spatial reuseduring the association phase which can be exploited to reduce collisionprobability among STAs during association phase.

FIG. 4 depicts a diagram of several beacon transmission intervals (BTI)according to an aspect of this disclosure, i.e. shows the AP TX and STARX training procedure (also called beacon transmission phase) assumingthat the STA has N different receive patterns which it intends to train.Each DMG (directional multi-gigabit) beacon frame that is transmitted ina BTI uses a dedicated direction or sector (i.e. a dedicated transmitbeam, also referred to as “third directive transmit beam” herein), whichis signaled within the DMG beacon. Thus, a STA receiving a DMG beaconcan retrieve the TX sector ID the AP used to transmit this particularbeacon.

The first step of the operation in the BTI described above may remainunchanged at the AP side, i.e. the AP transmits identification data viavarious directive beams 40 (“third directive transmit beams”). Incontrast to the known operation as described above, a STA listens withvarious directive receive beams 50 (“third directive receive beams”).Since the STA is not aligned to the frame structure at this point, a STAmay apply its directive receive beam 50 for the duration of at least onebeacon interval (BI). During the BI, the receive pattern shall beunchanged. The IEEE802.11ad standard defines the maximum duration of aBI up to 1000 ms, typical values are in the range of 100 ms. A STAlistens continuously to the channel and applies thereby its directivereceive patterns successively. After all directive receive patterns havebeen applied, either an AP has been detected (case A) or no AP has beendetected (case B).

In case A, the STA intends to communicate in a double directive A-BFT(DD-A-BFT) phase and the STA saves the best AP transmit sector (e.g. as“second transmit beam information”, also referred to as TX_(AP)) andbest STA receive sector (e.g. as “second receive beam information”, alsoreferred to as RX_(STA)) The best sector can be determined by evaluatingSNR, SINR, or link capacity for example.

A STA should only consider communicating within a DD-A-BFT underspecific conditions: e.g., if (i) the received SNR with sectors TX_(AP)and RX_(STA) is below a threshold, or (ii) the data reception inprevious BTI was not successful with a quasi-omni pattern, or (iii) thenumber of FailedRSSAttempts (number of unsuccessful associationattempts) in regular A-BFT with quasi-omni pattern is above a threshold,or (iv) too many collisions arise in regular A-BFT triggering the needfor spatial reuse in association phase. If the SNR is above thisthreshold, a STA shall consider a regular A-BFT. The threshold value indB may be defined by

γ_(target) +D _(STA,RX) +D _(AP,TX) −D _(STA,TX) −D _(AP,RX)

Thereby, γ_(target) target denotes the target SNR of the Control PHY MCSin dB, which is the most robust modulation coding scheme (MCS) and whichis applied in beamforming training. Furthermore, D denotes the beamdirectivity in dB of either STA or AP in either TX or RX mode,respectively.

In case B, no AP has been detected and the STA may repeat the listeningprocedure with various directive beams continuously or at a later pointin time.

It should be noted that the AP may perform no special operations duringthis training phase. The modifications are mainly on STA side.Therefore, this approach can reuse any BTI such as described inIEEE802.11ad and/or IEEE802.11ay BTI. No dedicated double directive orlong range BTI is required. Given that spatial reuse is the mainobjective of a STA, it may receive with an omni-directional patternduring a single BTI phase like it is done according to IEEE802.11ad.Prerequisite is that the link budget is sufficient to overcome pathloss.

In a second phase (also called association beamforming training phase),the STA TX and AP RX procedure takes place in various DD-A-BFT slots.During a single DD-A-BFT slot, the STA uses different transmit sectors,one for each SSW frame. The AP keeps its receiver pattern unchangedduring an entire DD-A-BFT slot, i.e. each SSW frame transmitted by theSTA within one DD-A-BFT slot shall be received by the AP with the samereceive beam or RX sector, respectively. Each DD-A-BFT slot usesdifferent AP receiver patterns. In contrast to known procedures, a STAtransmits SSW frames in all DD-A-BFT slots in order to cover allpossible beam combinations.

In case of reciprocity, the channel, the applied beams, and the antennasare independent and invariant with respect to the communicationdirection, i.e. TX and RX beams have same properties and are similar inpoint of main lobe directivity and HPBW; location of side lobes is notimportant as long as the side lobe attenuation is large enough). Channelreciprocity is a prerequisite for having beam and/or antenna reciprocitywhich is an implementation property. For this reason, beam and/orantenna reciprocity can be either on STA and/or AP side or it is notavailable at all, i.e. this property is device specific. In order tokeep the notation simple, the term reciprocity is used in the following.In case of single antenna systems, reciprocity includes channel and beamreciprocity. In case of multi-antenna systems antenna reciprocity is anadditional prerequisite.

First, the case shall be considered where reciprocity is availableneither at AP nor at STA side. FIG. 5 shows a diagram of a firstembodiment of association beamforming training with a single STA. Ineach of the DD-A-BFT slots, the AP listens with a directive beam 60, 62,respectively (“first directive receive beam”). Each DD-A-BFT slot mayhave a different beam 60, 62 (it may be beneficial to use same receivebeam in various DD-A-BFT slots, as will be explained later).

The STA is transmitting several SSW frames within one or more A-BFTslots, starting from the first A-BFT slot of the DD-A-BFT. In eachDD-A-BFT slot, a STA can sweep through M different transmit patterns,i.e. use different directive beams 70 (“first directive transmitbeams”). Thereby each SSW frame holds information about the bestreceived AP transmit sector (TX_(AP), “second transmit beaminformation”) determined in the BTI phase (see FIG. 4) and the currenttransmit sector of the STA. In order to receive the SSW feedback(“response”), a STA uses its best RX beam 71 as indicated by RX_(STA)(“second receive beam information”) determined earlier in the BTI phase.

The number of slots N and the number M of SSW frames per slot may besignaled in the beacon interval control field (see below) and determinedby the AP. In case a STA supports less than M transmit sectors, it shallstop transmission within the current slot after having completed all itstransmit patterns and continue in the next DD-A-BFT slot if necessary.In case a STA supports more than M transmit sectors, it shall transmitonly M selected sectors within a slot. The selection procedure is STAspecific and may comprise an angular interpolation between availablesectors.

In terms of the SSW feedback, the following rules are preferably appliedin an embodiment:

1. If the AP was able to decode a SSW frame sent by a STA, it transmitsa SSW feedback (“response”), preferably with TX sector information datacontained in the SSW frame (TX_(STA), “first transmit beam information”)and using a directive transmit beam 61 indicated by TX_(AP) (“secondtransmit beam information”).2. A SSW feedback is not sent if there has been no decodable SSW frameor if several STAs have been received simultaneously (collision). Acollision is defined as a SSW frame received from at least two STAssimultaneously. More than one valid SSW frame reception from more thanone STAs within a DD-A-BFT slot is not considered to be a collision butas feedback congestion. It shall be noted that some standards define acollision as two STAs using the same A-BFT slot even though the STAsaccess different SSW frames.3. In case more than one SSW frames from more than one different STAshave been received during a DD-A-BFT slot (feedback congestion), the SSWfeedback is addressed to the strongest STA. Pending SSW feedbacks may beaddressed in future DD-A-BFT slots within same DD-A-BFT. In this casethe same rule of sending the SSW feedback to the strongest STA applies.At the end of a DD-A-BFT phase, all pending SSW feedbacks shall beneglected.4. In case a STA received a SSW feedback, it stops transmitting infurther DD-A-BFT slots within the current BTI. This is to ensure thatDD-A-BFT slots can be used for further stations to associate.5. In case a STA received no feedback it may schedule transmission in afurther DD-A-BFT slot but keeps listening to the channel during all SSWfeedback phases of same DD-A-BFT phase. This is to ensure that a STA canreceive a SSW feedback frame at a later point in time in case offeedback congestion.

In FIG. 5 it is assumed that the AP receives a valid SSW frame in theN^(th) DD-A-BFT slot. Therefore, there is only one SSW feedback sent atthe end of the N^(th) DD-A-BFT slot.

In contrast to known operations, where STAs choose randomly a singleA-BFT slot for doing their sector sweep (in case a STA cannot finish itssector sweep, it may continue in the next slot), STAs transmit in someembodiments from the beginning of the first DD-A-BFT slot. Thelikelihood of a collision is reduced by the fact that the AP usesdirective receive beams, instead of an omni-directional pattern. Acollision arises if within one SSW frame interval of one DD-A-BFT slotsignals from two or more STAs have been received with similar power.Since the AP applies directive receive patterns, collision probabilityis lower compared to quasi-omni reception.

The above rule 3 applies, if the AP received more than one valid SSWframe from more than one STA. Because two frames have not been receivedat the same time, it is not a collision. At this point, the AP shouldsend two SSW feedbacks which may be not possible (as in IEEE 802.11adspecification) leading to feedback congestion which needs to beresolved. Therefore, the AP transmits to the STA received strongest (interms of SNR, SINR, or capacity for example) and the AP uses one of theupcoming SSW feedback opportunities to address the weak STA.Alternatively, frame structures to allow for simultaneous feedback tomultiple STAs can be envisioned. In this case, the SSW feedback may besent simultaneously to all or a set of the STAs that were receivedwithin the same DD-A-BFT slot.

FIG. 6 shows a diagram of a second embodiment of association beamformingtraining with a two STAs associating simultaneously. It is assumed thatSTA 1 and STA 2 have been able to associate in the first and secondDD-A-BFT slot, respectively. If a SSW feedback has been received, bothAP and STAs have knowledge of the best TX and RX sector ID to use forsubsequent communications. Note that only TX sector information isrequired to be exchanged between AP and STA during SSW frames and SSWfeedback, respectively.

In the example shown in FIG. 6, in a first sector sweep STA1 uses firstdirective transmit beams 70, STA2 uses first directive transmit beams 80and AP listens using a first directive receive beam 60. Preferably, inthe first directive transmit beams 70 and 80 the information about thebest third transmit beam used by the AP in the beacon transmissioninterval for the respective STA (i.e. TX_(AP)(STA1) and TX_(AP)(STA2),“second transmit beam information”) is included.

If during the first sweep the AP received a valid SSW frame only fromSTA1, it sends a SSW feedback (“response”) that is addressed to STA1using a second directive transmit beam 61 indicated by the secondtransmit beam information TX_(AP)(STA1) from STA1. Simultaneously, STA1and STA2 listen with the respective second directive receive beam 71, 81indicated by the second receive beam information RX_(STA1) andRX_(STA2). Since the SSW feedback is addressed to STA1, e.g. byincluding a corresponding identifier such as MAC address, AID(association identifier), or pre-AID, STA1 now knows its best sector(i.e. its best directive transmit beam) to use for subsequentcommunication since this information is included in the SSW feedbacktransmitted with 61. STA1 can now stop transmitting SSW frames insubsequent slots.

Subsequently, in a second sector sweep, STA2 uses first directivetransmit beams 80 AP listens using a first directive receive beam 62. Ifthe AP received a valid SSW frame from STA2 it sends a SSW feedback(“response”) that is addressed to STA2 and uses a second directivetransmit beam 63 indicated by the second transmit beam informationTX_(AP)(STA2) from STA2. Simultaneously, STA2 listens with therespective second directive receive beam 81 indicated by the secondreceive beam information RX_(STA2). Since the SSW feedback is addressedto STA2, e.g. by including a corresponding identifier, STA2 now knowsits best sector (i.e. its best directive transmit beam) to use forsubsequent communication since this information is included in the SSWfeedback 63. STA2 can now stop transmitting SSW frames in subsequentslots.

FIG. 7 shows a diagram of a third embodiment of association beamformingtraining with two STAs employing reciprocity. In this case, a STA hasalready the information about its best TX beam namely the best RX beam,i.e. TX_(STA)=RX_(STA) (equal sign should be inter-preted as describedabove). In this case, a STA transmits randomly only one SSW frame withineach DD-A-BFT slot using TX_(STA)=RX_(STA). This is to vacate theDD-A-BFT slots for other STAs competing for association in the same BI.FIG. 7 shows the basic procedure for two STAs (no collision or feedbackcongestion assumed). Dashed SSW frames indicate frames that are nottransmitted but are virtual placeholders (SSW frame transmitopportunities).

Furthermore, if it is known by the STA when the AP uses a particularreceived pattern and if the AP features reciprocity, it transmits onlyone SSW frame in each DD-A-BFT slot where the AP receives with thedesired receive beam. Since the STA knows best TX_(AP) sector, it isalso aware of the best RX_(AP) sector (TX_(AP)=RX_(AP)). If the sweepsequence of TX and RX beams is equal, the STA can predict, when the APapplies the appropriate receive pattern in DD-A-BFT. Alternatively, theRx sectors, which the AP is going to use in DD-A-BFT, can be signaledwithin the DMG beacon. In this case, a single STA can occupy randomlyeven only one SSW slot within all DD-A-BFT slots during a BI. However,for more robustness, a single STA can occupy several SSW slots in orderto train more (e.g. neighboring) RX sectors at AP and/or it can use moreSSW frames within a slot in order to train more of its own TX sectors(e.g. TX sectors that are neighbors of the RX sectors on which thehighest SNR was received during the AP SSW in BTI).

If the AP features reciprocity but the STA does not, a STA transmitsonly in that single slot where the AP applies the appropriate receivesector, i.e. RX_(AP)=TX_(AP). This requires the STA to be aware in whichslot the AP applies a dedicated receive sector.

It should be noted that all four variants—no reciprocity, STAreciprocity, AP reciprocity, AP and STA reciprocity—can be appliedindependently and simultaneously. There is no requirement that allassociating STAs have same properties or access rules.

In current IEEE 802.11ad specification, an AP supports only around-trip-time delay of 1 μs, which corresponds to a maximum range of150 m. It is proposed to change this value to multiples of 1 μs usinge.g. the “Coverage Class field” as defined in the IEEE 802.11 standard.At the moment this field is not applicable for mmWave communication.

All variable parameters may be signaled in the Beacon Interval Controlfield shown in FIG. 8, which is part of DMG beacon frame body. Forexample: A-BFT length field indicates the number of A-BFT slots (1 up to8); FSS indicates the number of SSW frame slots within one A-BFT slot (1up to 16); Next A-BFT field indicates the number of BI during which theA-BFT is not present; N BIs A-BFT field indicates the interval, innumber of beacon intervals, at which the AP allocates an A-BFT. Allother fields are described the IEEE 802.11 standard.

For DD-A-BFT, the minimal change required is an indication if theupcoming A-BFT is a DD-A-BFT. It is proposed to use a single bit of thereserved bits (B44 to B47 in FIG. 8) to indicate a DD-A-BFT.

A further option to signal a DD-A-BFT is to add a further control fieldin the DMG beacon frame body shown in FIG. 9. The DMG beacon frame bodycan hold several partly optional signaling fields and therefore itslength is variable. Thus, several options to signal a DD-A-BFT can bepossibly implemented:

-   -   Introduction of a simple DD-A-BFT control field with the        structure show in FIG. 10.    -   DD-A-BFT length field indicates the number of DD-A-BFT slots (1        up to 8).    -   FSS field indicates the number of SSW frame slots within one        DD-A-BFT slot (1 up to 16).    -   Next DD-A-BFT field indicates the number of BI during which the        DD-A-BFT is not present.    -   DD-A-BFT count field indicates the number of DD-A-BFTs since the        STA sending the DMG Beacon frame last switched RX DMG antennas        for a DD-A-BFT. A value of 0 indicates that the DMG antenna used        in the forthcoming DD-A-BFT differs from the DMG antenna used in        the last DD-A-BFT.    -   N-DD-A-BFT in Ant field indicates how many A-BFTs the STA        sending the DMG Beacon frame receives from each DMG antenna.    -   Introduction of an advanced DD-A-BFT control field (see FIG.        11), which enables the AP to use several DD-A-BFT phases to        train all receive sectors in case number of beams to be tested        is larger than the number of DD-A-BFT slots as signaled in        DD-A-BFT length field. This is indicated by ‘fragmented DD-A-BFT        bit. The number of required DD-A-BFT slots is indicated by        DD-A-BFT span’.

If it is assumed that there is a total of N non-overlapping receivepatterns, each receive pattern can contribute a gain of roughly 10log₁₀N dB of link budget which results in √N fold link distanceaccording to the free space path loss formula for example.

Further if N different non-overlapping receive patterns are assumed,collision probability of STAs joining at same time can be reduced byfactor N, if STAs are assumed to be equally spatially distributed.

By use communication devices and methods according to the presentdisclosure several advantages can be achieved. In particular: long rangeAP discovery for mmWave systems; increase of roughly 10 log₁₀M dB inlink budget in association phase; improved channel access in case ofreciprocity; and spatial reuse in association phase, i.e. spatial beamproperties are exploited for association phase

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. As will be understood by thoseskilled in the art, the present disclosure may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentdisclosure is intended to be illustrative, but not limiting of the scopeof the disclosure, as well as other claims. The disclosure, includingany readily discernible variants of the teachings herein, defines, inpart, the scope of the foregoing claim terminology such that noinventive subject matter is dedicated to the public.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single element or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measures cannot be used to advantage.

In so far as embodiments of the disclosure have been described as beingimplemented, at least in part, by software-controlled data processingapparatus, it will be appreciated that a non-transitory machine-readablemedium carrying such software, such as an optical disk, a magnetic disk,semiconductor memory or the like, is also considered to represent anembodiment of the present disclosure. Further, such a software may alsobe distributed in other forms, such as via the Internet or other wiredor wireless telecommunication systems.

The elements of the disclosed devices, apparatus and systems may beimplemented by corresponding hardware and/or software elements, forinstance appropriated circuits. A circuit is a structural assemblage ofelectronic components including conventional circuit elements,integrated circuits including application specific integrated circuits,standard integrated circuits, application specific standard products,and field programmable gate arrays. Further a circuit includes centralprocessing units, graphics processing units, and microprocessors whichare programmed or configured according to software code. A circuit doesnot include pure software, although a circuit includes theabove-described hardware executing software.

It follows a list of further embodiments of the disclosed subjectmatter:

-   1. A communication device (1) for RF-based communication with    another communication device (2), said communication device (1)    comprising:    -   an antenna circuitry (10) configured to transmit and receive RF        signals, and    -   a beamforming circuitry (11) configured to perform beamforming        and to control the antenna circuitry in a beamforming training        phase to transmit and/or receive RF signals using one or more        selected directive beams, wherein the beamforming circuitry (11)        is configured to perform beamforming training by controlling the        antenna circuitry        -   i) to transmit data using at least one first directive            transmit beam, wherein the other communication device (2) is            configured to listen using a first directive receive beam,            said data including a second transmit beam information, and        -   ii) to subsequently listen using a predetermined second            directive receive beam for a response from the other            communication device (2), which is configured to transmit,            if the data transmitted in step i) have been received, a            response using a second directive transmit beam indicated by            the second transmit beam information.-   2. The communication device as defined in any one of the preceding    embodiments,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry to successively transmit the data in step i) with    a number of different first directive transmit beams.-   3. The communication device as defined in embodiment 2,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry to transmit a predefined number of first directive    beams as signaled by the other communication device in a previous    training phase or a beacon transmission phase.-   4. The communication device as defined in embodiment 2 or 3,    wherein the beamforming circuitry (11) is configured to obtain from    the response received in step ii) a first transmit beam information    indicating at least one of the first directive transmit beams by    which the data, which have been received by the second communication    device (2), have been transmitted by the communication device (1).-   5. The communication device as defined in any one of the preceding    embodiments,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry to transmit the data in step i) with a single    first directive transmit beam.-   6. The communication device as defined in embodiment 5,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry to transmit the data in step i) with the same or    different single first directive transmit beams in subsequent    iterations of step i).-   7. The communication device as defined in embodiment 5 or 6,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry to use the same beam as first directive transmit    beam and second directive receive beam.-   8. The communication device as defined in any one of the preceding    embodiments,    wherein the beamforming circuitry (11) is configured to decide in    step ii) that a response has been received if it includes a first    identifier of the communication device (1).-   9. The communication device as defined in any one of the preceding    embodiments,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry to carry out, in a beacon transmission phase prior    to the beamforming training phase, the steps of    a) listening using a third receive beam while the other    communication device (2) transmits a second identifier of the other    communication device (2) subsequently using different third    directive transmit beams, and    b) setting, once the second identifier has been received, the third    directive transmit beam used for transmitting the second identifier    as second directive transmit beam indicated by the second transmit    beam information.-   10. The communication device as defined in embodiment 9,    wherein the beamforming circuitry (11) is configured to control the    antenna circuitry    -   to listen, in step a), by successively using different third        directive receive beams, while in each succession the other        communication device (2) subsequently uses different third        directive transmit beams and    -   by setting, in step b), the third directive receive beam with        which the second identifier has been received, as second        directive receive beam.-   11. A communication method for RF-based communication with another    communication device (2), said communication method controlling an    antenna circuitry in a beamforming training phase to transmit and/or    receive RF signals using one or more selected directive beams by-   i) transmitting data using at least one first directive transmit    beam, wherein the other communication device (2) is configured to    listen using a first directive receive beam, said data including a    second transmit beam information, and-   ii) subsequently listening using a predetermined second directive    receive beam for a response from the other communication device (2),    which is configured to transmit, if the data transmitted in step i)    have been received, a response using a second directive transmit    beam indicated by the second transmit beam information.-   12. A communication device (2) for RF-based communication with    another communication device (1), said communication device (2)    comprising:    -   an antenna circuitry (20) configured to transmit and receive RF        signals, and    -   a beamforming circuitry (21) configured to perform beamforming        and to control the antenna circuitry, in a beamforming training        phase, to transmit and/or receive RF signals using one or more        selected directive beams, wherein the beamforming circuitry (21)        is configured to perform beamforming training by controlling the        antenna circuitry        -   i) to listen using a first directive receive beam for data            transmitted by the other communication device (1) using at            least one first directive transmit beam, said data including            a second transmit beam information, and        -   ii) to subsequently transmit, if the data transmitted in            step i) have been received, a response using a second            directive transmit beam indicated by the second transmit            beam information, wherein the other communication device (1)            is configured to listen using a predetermined second            directive receive beam.-   13. The communication device as defined in embodiment 12,    wherein the beamforming circuitry (21) is configured to include in    the response a first transmit beam information indicating the first    directive transmit beam by which the data, which have been received    by the communication device (2), have been transmitted by the other    communication device (1).-   14. The communication device as defined in embodiment 12 or 13,    wherein the beamforming circuitry (21) is configured to control the    antenna circuitry to include in the response a first identifier of    the other communication device (1) from which the data have been    received.-   15. The communication device as defined in embodiment 14,    wherein the beamforming circuitry (21) is configured to control the    antenna circuitry to include in the response a first identifier of    another communication device from which the data have been received    with highest quality or SNR.-   16. The communication device as defined in any one of the    embodiments 12 to 15,    wherein the beamforming circuitry (21) is configured to control the    antenna circuitry to transmit a response only if data have been    received in step i) with a quality or SNR above a predetermined    threshold.-   17. The communication device as defined in any one of the    embodiments 12 to 15,    wherein the beamforming circuitry (21) is configured to control the    antenna circuitry to perform beacon transmission, prior to    beamforming training, by transmitting a second identifier of the    second communication device (2) subsequently using different third    directive transmit beams, while the other communication device (1)    is configured to listen using a third receive beam.-   18. The communication device as defined in any one of the    embodiments 12 to 15,    wherein the beamforming circuitry (21) is configured to maintain an    ordered list of other communication devices and their respective    first transmit beam information from which data have successfully    been received and/or wherein the beamforming circuitry (21) is    configured to control the antenna circuitry to include in the    response one identifier and first transmit beam information of the    ordered list while removing this data from the ordered list.-   19. A communication method for RF-based communication with another    communication device (1), said communication method controlling an    antenna circuitry, in a beamforming training phase, to transmit    and/or receive RF signals using one or more selected directive beams    by    i) listening using a first directive receive beam for data    transmitted by the other communication device (1) using at least one    first directive transmit beam, said data including a second transmit    beam information, and    ii) subsequently transmitting, if the data transmitted in step i)    have been received, a response using a second directive transmit    beam indicated by the second transmit beam information, wherein the    other communication device (1) is configured to listen using a    predetermined second directive receive beam.-   20. A non-transitory computer-readable recording medium that stores    therein a computer program product, which, when executed by a    processor, causes the method according to embodiment 11 or 19 to be    performed.-   21. A computer program comprising program code means for causing a    computer to perform the steps of said method according to embodiment    11 or 19 when said computer pro-gram is carried out on a computer.-   22. The communication device as defined in any one of embodiments 1    to 10,    wherein the beamforming circuitry (11) is configured to repeat    steps i) and ii) if no response is received in step ii).-   23. The communication device as defined in any one of embodiments 12    to 18,    wherein the beamforming circuitry (21) is configured to repeat    steps i) and ii) by using different first predetermined directive    receive beams in step i).

1. A communication device for RF-based communication with anothercommunication device, said communication device comprising: an antennacircuitry configured to transmit and receive RF signals, and abeamforming circuitry configured to perform beamforming and to controlthe antenna circuitry in a beamforming training phase to transmit and/orreceive RF signals using one or more selected directive beams, whereinthe beamforming circuitry is configured to perform beamforming trainingby controlling the antenna circuitry i) to transmit data using at leastone first directive transmit beam, wherein the other communicationdevice is configured to listen using a first directive receive beam,said data including a second transmit beam information, and ii) tosubsequently listen using a predetermined second directive receive beamfor a response from the other communication device, which is configuredto transmit, if the data transmitted in step i) have been received, aresponse using a second directive transmit beam indicated by the secondtransmit beam information.
 2. The communication device as claimed inclaim 1, wherein the beamforming circuitry is configured to control theantenna circuitry to successively transmit the data in step i) with anumber of different first directive transmit beams.
 3. The communicationdevice as claimed in claim 2, wherein the beamforming circuitry isconfigured to control the antenna circuitry to transmit a predefinednumber of first directive beams as signaled by the other communicationdevice in a previous training phase or a beacon transmission phase. 4.The communication device as claimed in claim 2, wherein the beamformingcircuitry is configured to obtain from the response received in step ii)a first transmit beam information indicating at least one of the firstdirective transmit beams by which the data, which have been received bythe second communication device, have been transmitted by thecommunication device.
 5. The communication device as claimed in claim 1,wherein the beamforming circuitry is configured to control the antennacircuitry to transmit the data in step i) with a single first directivetransmit beam.
 6. The communication device as claimed in claim 5,wherein the beamforming circuitry is configured to control the antennacircuitry to transmit the data in step i) with the same or differentsingle first directive transmit beams in subsequent iterations of stepi).
 7. The communication device as claimed in claim 5, wherein thebeamforming circuitry is configured to control the antenna circuitry touse the same beam as first directive transmit beam and second directivereceive beam.
 8. The communication device as claimed in claim 1, whereinthe beamforming circuitry is configured to decide in step ii) that aresponse has been received if it includes a first identifier of thecommunication device and/or to repeat steps i) and ii) if no response isreceived in step ii).
 9. The communication device as claimed in claim 1,wherein the beamforming circuitry is configured to control the antennacircuitry to carry out, in a beacon transmission phase prior to thebeamforming training phase, the steps of a) listening using a thirdreceive beam while the other communication device transmits a secondidentifier of the other communication device subsequently usingdifferent third directive transmit beams, and b) setting, once thesecond identifier has been received, the third directive transmit beamused for transmitting the second identifier as second directive transmitbeam indicated by the second transmit beam information.
 10. Thecommunication device as claimed in claim 9, wherein the beamformingcircuitry is configured to control the antenna circuitry to listen, instep a), by successively using different third directive receive beams,while in each succession the other communication device subsequentlyuses different third directive transmit beams and by setting, in stepb), the third directive receive beam with which the second identifierhas been received, as second directive receive beam.
 11. A communicationmethod for RF-based communication with another communication device,said communication method controlling an antenna circuitry in abeamforming training phase to transmit and/or receive RF signals usingone or more selected directive beams by i) transmitting data using atleast one first directive transmit beam, wherein the other communicationdevice is configured to listen using a first directive receive beam,said data including a second transmit beam information, and ii)subsequently listening using a predetermined second directive receivebeam for a response from the other communication device, which isconfigured to transmit, if the data transmitted in step i) have beenreceived, a response using a second directive transmit beam indicated bythe second transmit beam information.
 12. A communication device forRF-based communication with another communication device, saidcommunication device comprising: an antenna circuitry configured totransmit and receive RF signals, and a beamforming circuitry configuredto perform beamforming and to control the antenna circuitry, in abeamforming training phase, to transmit and/or receive RF signals usingone or more selected directive beams, wherein the beamforming circuitryis configured to perform beamforming training by controlling the antennacircuitry i) to listen using a first directive receive beam for datatransmitted by the other communication device using at least one firstdirective transmit beam, said data including a second transmit beaminformation, and ii) to subsequently transmit, if the data transmittedin step i) have been received, a response using a second directivetransmit beam indicated by the second transmit beam information, whereinthe other communication device is configured to listen using apredetermined second directive receive beam.
 13. The communicationdevice as claimed in claim 12, wherein the beamforming circuitry isconfigured to include in the response a first transmit beam informationindicating the first directive transmit beam by which the data, whichhave been received by the communication device, have been transmitted bythe other communication device.
 14. The communication device as claimedin claim 12, wherein the beamforming circuitry is configured to controlthe antenna circuitry to include in the response a first identifier ofthe other communication device from which the data have been received.15. The communication device as claimed in claim 14, wherein thebeamforming circuitry is configured to control the antenna circuitry toinclude in the response a first identifier of another communicationdevice from which the data have been received with highest quality orSNR.
 16. The communication device as claimed in claim 12, wherein thebeamforming circuitry is configured to control the antenna circuitry totransmit a response only if data have been received in step i) with aquality or SNR above a predetermined threshold and/or to repeat steps i)and ii) by using different first predetermined directive receive beamsin step i).
 17. The communication device as claimed in claim 12, whereinthe beamforming circuitry is configured to control the antenna circuitryto perform beacon transmission, prior to beamforming training, bytransmitting a second identifier of the second communication devicesubsequently using different third directive transmit beams, while theother communication device is configured to listen using a third receivebeam.
 18. The communication device as claimed in claim 12, wherein thebeamforming circuitry is configured to maintain an ordered list of othercommunication devices and their respective first transmit beaminformation from which data have successfully been received and/orwherein the beamforming circuitry is configured to control the antennacircuitry to include in the response one identifier and first transmitbeam information of the ordered list while removing this data from theordered list.
 19. A communication method for RF-based communication withanother communication device, said communication method controlling anantenna circuitry, in a beamforming training phase, to transmit and/orreceive RF signals using one or more selected directive beams by i)listening using a first directive receive beam for data transmitted bythe other communication device using at least one first directivetransmit beam, said data including a second transmit beam information,and ii) subsequently transmitting, if the data transmitted in step i)have been received, a response using a second directive transmit beamindicated by the second transmit beam information, wherein the othercommunication device is configured to listen using a predeterminedsecond directive receive beam.
 20. A non-transitory computer-readablerecording medium that stores therein a computer program product, which,when executed by a processor, causes the method according to claim 11 tobe performed.